That Phantom Flush Is Costing You Money
A toilet that runs constantly — or starts and stops on its own throughout the day — isn't just annoying. It can waste up to 200 litres of water every single day, adding £200–£400 to your annual water bill. The fix is almost always simple, cheap, and something you can do in under 30 minutes.
Understanding How a Toilet Works
There are two main mechanisms inside your cistern (the tank at the back). The fill valve refills the tank after each flush. The flapper is a rubber seal at the bottom of the tank that holds water in until you flush. When either fails, water runs continuously into the bowl.
Step 1: Diagnose the Problem
Remove the cistern lid and look inside. If water is trickling over the top of the overflow tube, the fill valve needs adjusting. If the water level looks normal but you can still hear running, the flapper is the culprit.
The dye test: drop food colouring into the cistern. Wait 15 minutes without flushing. If colour appears in the bowl, your flapper is leaking.
Step 2: Fix the Flapper (Most Common Fix)
Turn off the water supply using the shutoff valve behind the toilet (turn clockwise). Flush to empty the tank. The flapper is the rubber seal at the bottom connected to a chain. Unhook the chain from the flush handle arm and slip the flapper off its ears. Take it to the hardware store and match the size. Fit the new one, re-attach the chain with a little slack, turn water back on, and test.
Total cost: £3–6. Time: 15 minutes.
Step 3: Adjust the Float (If Water Is Too High)
If water is running into the overflow tube, the float is set too high. On a ball-float system (older design), bend the arm slightly downward. On a cup-float system (modern column-style), pinch the adjustment clip and slide the float down. The water level should sit about 2.5cm below the top of the overflow tube.
Step 4: Replace the Fill Valve
If adjusting the float doesn't solve it, the fill valve itself may be worn. Turn off water, empty the tank, disconnect the water supply line from under the cistern. Unscrew the locknut, pull out the old valve, drop in the new one (universal fill valves cost around £8–12), tighten the locknut, reconnect the supply line, and turn water back on.
When to Call a Plumber
If you notice cracks in the porcelain or the base of the toilet is leaking, it's time for a professional. But in 9 out of 10 cases, a £5 flapper and 20 minutes is all you need.